Limited echelette lens, systems and methods

ABSTRACT

An ophthalmic lens with a circular surface structure and limited adjacent echelettes that provides enhanced image quality across an extended range of foci.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to U.S. patent application Ser. No.13/934,556, now U.S. Pat. No. 8,820,927 which issued on Sep. 2, 2014,which claims priority to U.S. patent application Ser. No. 12/971,607,now U.S. Pat. No 8,480,228 which issued on Jul. 9, 2013, which claimspriority under 35 U.S.C §119(e) to provisional application No.61/288,255 filed on Dec. 18, 2009, the entire contents of all of whichare incorporated herein by reference. This application is related to thefollowing applications which were filed concurrently herewith: SingleMicrostructure Lens, Systems And Methods, U.S. patent application Ser.No.: 12/971,506, filed on Dec. 17, 2010; Ophthalmic Lens, Systems AndMethods With Angular Varying Phase Delay, U.S. patent application Ser.No.: 12/971,889, filed on Dec. 17, 2010; and Ophthalmic Lens, SystemsAnd Methods Having At Least One Rotationally Asymmetric DiffractiveStructure, U.S. patent application Ser. No.: 61/424,433, filed on Dec.17, 2010. The entire contents of these three applications are alsoincorporated herein by reference. This application is also related tothe following U.S. patent application Ser. Nos.: 61/047,699 and12/109,251, both filed on Apr. 24, 2008; Ser. No. 12/429,155 filed onApr. 23, 2009; Ser. No. 12/372,573 filed on Feb. 17, 2009; Ser. No.12/197,249 filed on Aug. 23, 2008; Ser. No. 12/120,201 filed on Apr. 13,2008, and Ser. No. 12/771,550 filed on Apr. 30, 2010.

BACKGROUND OF THE INVENTION

Embodiments of the present invention relate to vision treatmenttechniques and in particular, to ophthalmic lenses such as, for example,contact lenses, corneal inlays or onlays, or intraocular lenses (IOLs)including, for example, phakic IOLs and piggyback IOLs (i.e. IOLsimplanted in an eye already having an IOL).

Presbyopia is a condition that affects the accommodation properties ofthe eye. As objects move closer to a young, properly functioning eye,the effects of ciliary muscle contraction and zonular relaxation allowthe lens of the eye to change shape, and thus increase its optical powerand ability to focus at near distances. This accommodation can allow theeye to focus and refocus between near and far objects.

Presbyopia normally develops as a person ages, and is associated with anatural progressive loss of accommodation. The presbyopic eye oftenloses the ability to rapidly and easily refocus on objects at varyingdistances. The effects of presbyopia usually become noticeable after theage of 45 years. By the age of 65 years, the crystalline lens has oftenlost almost all elastic properties and has only limited ability tochange shape.

Along with reductions in accommodation of the eye, age may also induceclouding of the lens due to the formation of a cataract. A cataract mayform in the hard central nucleus of the lens, in the softer peripheralcortical portion of the lens, or at the back of the lens. Cataracts canbe treated by the replacement of the cloudy natural lens with anartificial lens. An artificial lens replaces the natural lens in theeye, with the artificial lens often being referred to as an intraocularlens or “IOL”.

Monofocal IOLs are intended to provide vision correction at one distanceonly, usually the far focus. Predicting the most appropriate IOL powerfor implantation has limited accuracy, and an inappropriate IOL powercan leave patients with residual refraction following surgery.Accordingly, it may be necessary for a patient who has received an IOLimplant to also wear spectacles to achieve good far vision. At the veryleast, since a monofocal IOL provides vision treatment at only onedistance and since the typical correction is for far distance,spectacles are usually needed for good near vision and sometimesintermediate vision. The term “near vision” generally corresponds tovision provided when objects are at a distance from the subject eye ofbetween about 1 to 2 feet are substantially in focus on the retina ofthe eye. The term “distant vision” generally corresponds to visionprovided when objects at a distance of at least about 6 feet or greaterare substantially in focus on the retina of the eye. The term“intermediate vision” corresponds to vision provided when objects at adistance of about 2 feet to about 5 feet from the subject eye aresubstantially in focus on the retina of the eye.

There have been various attempts to address limitations associated withmonofocal IOLs. For example, multifocal IOLs have been proposed thatdeliver, in principle, two foci, one near and one far, optionally withsome degree of intermediate focus. Such multifocal or bifocal IOLs areintended to provide good vision at two distances, and include bothrefractive and diffractive multifocal IOLs. In some instances, amultifocal IOL intended to correct vision at two distances may provide anear add power of about 3.5 or 4.0 diopters.

Multifocal IOLs may, for example, rely on a diffractive optical surfaceto direct portions of the light energy toward differing focal distances,thereby allowing the patient to clearly see both near and far objects.Multifocal ophthalmic lenses (including contact lenses or the like) havealso been proposed for treatment of presbyopia without removal of thenatural crystalline lens. Diffractive optical surfaces, either monofocalor multifocal, may also be configured to provide reduced chromaticaberration.

Diffractive monofocal and multifocal lenses can make use of a materialhaving a given refractive index and a surface curvature which provide arefractive power. Diffractive lenses have a diffractive profile whichconfers the lens with a diffractive power that contributes to theoverall optical power of the lens. The diffractive profile is typicallycharacterized by a number of diffractive zones. When used for ophthalmiclenses these zones are typically annular lens zones, or echelettes,spaced about the optical axis of the lens. Each echelette may be definedby an optical zone, a transition zone between the optical zone and anoptical zone of an adjacent echelette, and an echelette geometry. Theechelette geometry includes an inner and outer diameter and a shape orslope of the optical zone, a height or step height, and a shape of thetransition zone. The surface area or diameter of the echelettes largelydetermines the diffractive power(s) of the lens and the step height ofthe transition between echelettes largely determines the lightdistribution between the different add powers. Together, theseechelettes form a diffractive profile.

A multifocal diffractive profile of the lens may be used to mitigatepresbyopia by providing two or more optical powers; for example, one fornear vision and one for far vision. The lenses may also take the form ofan intraocular lens placed within the capsular bag of the eye, replacingthe original lens, or placed in front of the natural crystalline lens.The lenses may be in the form of a contact lens, most commonly a bifocalcontact lens, or in any other form mentioned herein.

Although multifocal ophthalmic lenses lead to improved quality of visionfor many patients, additional improvements would be beneficial. Forexample, some pseudophakic patients experience undesirable visualeffects (dysphotopsia), e.g. glare or halos. Halos may arise when lightfrom the unused focal image creates an out-of-focus image that issuperimposed on the used focal image. For example, if light from adistant point source is imaged onto the retina by the distant focus of abifocal IOL, the near focus of the IOL will simultaneously superimpose adefocused image on top of the image formed by the distant focus. Thisdefocused image may manifest itself in the form of a ring of lightsurrounding the in-focus image, and is referred to as a halo. Anotherarea of improvement revolves around the typical bifocality of multifocallenses. Since multifocal ophthalmic lenses typically provide for nearand far vision, intermediate vision may be compromised.

A lens with an extended depth of focus may provide certain patients thebenefits of good vision at a range of distances, while having reduced orno dysphotopsia. Various techniques for extending the depth of focus ofan IOL have been proposed. For example, some approaches are based on abulls-eye refractive principle, and involve a central zone with aslightly increased power. Other techniques include an asphere or includerefractive zones with different refractive zonal powers.

Although certain proposed treatments may provide some benefit topatients in need thereof, still further advances would be desirable. Forexample, it would be desirable to provide improved IOL systems andmethods that confer enhanced image quality across a wide and extendedrange of foci without dysphotopsia. Embodiments of the present inventionprovide solutions that address the problems described above, and henceprovide answers to at least some of these outstanding needs.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention generally provide improved lensesand imaging techniques. Exemplary embodiments provide improvedophthalmic lenses (such as, for example, contact lenses, corneal inlaysor onlays, or intraocular lenses (IOLs) including, for example, phakicIOLs and piggyback IOLs) and associated methods for their design anduse.

Embodiments of the present invention encompass IOL optics having acircular surface structure with one to four echelettes surrounding thesurface structure. The profile is designed such that it increases thedepth of focus of the pseudophakic eye, where the natural crystallinelens of the eye is substituted with a synthetic lens. Such limited ringIOL techniques suppress the distinct bifocality associated withtraditional multifocal IOLs which have many diffractive rings.Consequently, dysphotopsia (e.g., halo effects) associated withtraditional multifocal IOLs can be alleviated by lenses according toembodiments of the present invention.

An exemplary limited ring IOL includes an anterior face and a posteriorface. A profile can be imposed on the anterior or posterior surface orface. The profile can have an inner portion and an outer portion. Theinner portion typically presents a parabolic curved shape. The innerportion may also be referred to as a microstructure, or a central orinner echelette. Between the inner portion and the outer portion, theremay be a transition zone that connects the inner and outer portions. Theouter portion may be comprised of four or fewer echelettes.

In addition to parabolic shapes, the central/inner echelette can haveany of a variety of shapes including hyperbolic, spherical, aspheric,and sinusoidal. The transition between the inner and outer portions ofthe central/inner echelette can be a sharp transition, or it can be asmooth transition.

The surface of the outer portion at the outside of the microstructurecan have any spherical or aspherical shape and is comprised of a limitednumber of echelettes, preferably less than four. The shape of the outerportion can be optimized for having the desired optical performance fora range of pupil sizes. The desired optical performance can be based onelements such as the depth of focus, the optical quality in the farfocus, and the change in best focus (or far focus) position as afunction of the pupil size. Optimization rules may be applied as if theshape were a refractive monofocal IOL, or a refractive IOL having anextended depth of focus, or a refractive design that corrects ormodifies the ocular spherical aberration. Specific designs can be madein which the interplay between the central echelette and the outer zoneis incorporated in the design or optimization. The techniques describedherein are well suited for implementation with any of a variety ofophthalmic lenses, including IOLs, corneal inlays or onlays, and/orcontact lenses.

In one aspect, embodiments of the present invention encompass ophthalmiclens systems and methods for treating an eye of a patient. An exemplarylens may include an anterior face with an anterior refractive profileand a posterior face with a posterior refractive profile. The faces maybe disposed about an optical axis. The lens may also include adiffractive profile imposed on the anterior refractive profile or theposterior refractive profile. In some cases, the diffractive profile mayinclude no more than 5 echelettes. Optionally, the central echelette canbe disposed within a central zone of the lens. Relatedly, the centralechelette may be disposed within an annular ring surrounding a centralrefractive zone of the lens. In some cases, the lens includes aperipheral zone with a limited number of echelettes that surround thecentral echelette or annular ring. The limited number of echelettes maybe characterized by a constant phase shift.

According to some embodiments, an ophthalmic lens can include a limitednumber of echelettes that are characterized by parabolic curves. Thecentral echelette can have a diameter within a range from about 1 mm toabout 4 mm. For example, the central echelette may have a diameter ofabout 1.5 mm. In some cases, the central echelette can have a diameterwithin a range from about 1.0 mm to about 5.0 mm. Lens embodiments mayinclude a peripheral portion comprised of a limited number of echelettesand a refractive portion. Central and peripheral echelettes can have asurface area that is between 1 and 7 mm². For example, the echelettesmay have a surface area that is 2.3 mm². In some cases, a lens mayinclude a peripheral portion which surrounds the echelettes. A lens mayinclude a peripheral portion having an outer diameter within a rangefrom about 4 mm to about 6 mm. In some cases, the peripheral portionwill have an outer diameter within a range of about 1 mm to about 7 mm.For example, a lens may include a peripheral portion having an outerdiameter of about 5 mm.

The echelettes may be characterized by a step height having a valuewithin a range from about 0.5 μm and about 4 μm. According to someembodiments, a transition can be characterized by a step height having avalue within a range of about 1.5 μm and 2.5 μm. According to someembodiments, a transition can be characterized by a step height having avalue of about 1.7 μm. In other embodiments, the step height may have avalue of about 2.0 μm.

Optionally, a diffractive profile can be characterized by a designwavelength, and a lens can include a transition characterized by a stepheight producing a phase shift between about 0.25 and about 1 times thedesign wavelength. In some cases, a diffractive profile can becharacterized by a design wavelength, and the lens can include atransition characterized by a step height producing a phase shiftbetween about 0.15 and about 2 times the design wavelength.

In some aspects, embodiments of the present invention encompass systemsand methods involving an ophthalmic lens that include an anterior facewith an anterior refractive profile and a posterior face with aposterior refractive profile, such that the faces are disposed about anoptical axis, and a diffractive profile imposed on the anteriorrefractive profile or the posterior refractive profile, such that thediffractive profile includes an inner echelette and four or fewer outerechelettes. According to some embodiments, an inner echelette can bedisposed within a central zone of the lens. In some cases, an innerechelette can be disposed within an annular ring surrounding a centralzone of the lens. Optionally, an inner echelette and outer echelettescan be characterized by a parabolic curve. In some cases, an innerechelette and outer echelettes can be characterized by a constant phaseshift. According to some embodiments, an ophthalmic lens may include anaccommodating lens and/or a multifocal lens.

For a fuller understanding of the nature and advantages of the presentinvention, reference should be had to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view of an eye with a multifocal refractiveintraocular lens.

FIG. 1B is a cross-sectional view of an eye having an implantedmultifocal diffractive intraocular lens.

FIG. 2A is a front view of a diffractive multifocal ophthalmic lens.

FIG. 2B is a cross-sectional view of the lens of FIG. 2A.

FIGS. 3A-3B are a graphical representations of a portion of thediffractive profile of a conventional diffractive multifocal lens.

FIG. 4 shows aspects of the central echelette of a lens according toembodiments of the present invention.

FIG. 4A-4E illustrates aspects of a lens profile according toembodiments of the present invention.

FIG. 5 shows aspects of calculated defocus curves according to a centralechelette embodiment.

FIG. 6 shows aspects of calculated defocus curves according to aembodiments of the present invention.

For illustration purposes, the profile geometries shown in certainaforementioned figures were not drawn exactly to scale. The heights ofthe profiles shown in the figures are generally on the order of about0.1 μm to about 8.0 μm although the heights may vary depending onfactors such as the amount of correction needed by the patient, therefractive index of the lens material and surrounding medium, and thedesired distribution of light between wanted diffraction orders.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that the figures and descriptions of the presentinvention have been simplified to illustrate elements that are relevantfor a clear understanding of the present invention, while eliminating,for the purpose of clarity and brevity, many other elements found intypical ophthalmic lenses, implantable optic apparatuses, systems andmethods. Those of ordinary skill in the art may thus recognize thatother elements and/or steps are desirable and/or required inimplementing the present invention. However, because such elements andsteps are well known in the art, and because they do not facilitate abetter understanding of the present invention, a discussion of suchelements and steps is not provided herein. The disclosure herein isdirected to all such variations and modifications to the disclosedelements and methods known to those skilled in the art.

Embodiments of the present invention encompass systems and methods thatprovide improved image quality over an extended range of focal points orfoci. Systems and methods disclosed herein can encompass variousophthalmic lenses such as, for example, contact lenses, intraocularlenses, spectacle lenses, and corneal inlays or onlays. Exemplaryembodiments include ophthalmic lenses having an extended depth of focus,as compared to conventional monofocal lenses, and reduced dysphtopsia ascompared to conventional multifocal ophthalmic lenses. In some cases,such techniques involve an IOL approach that includes a limited numberof rings or echelettes, and typically involves an expanded depth offocus. Advantageously, such approaches can provide a patient with gooddistance vision, as well as good vision at intermediate distanceswithout dysphotopsia.

Embodiments of the present invention generally provide improved lensesand imaging systems and may be incorporated into any system in which alens with an extended depth of focus may be advantageous, such ascamera/video lenses, including those used for surveillance or forsurgical procedures, as well as for cameras in mobile phones or otherrelated devices. Embodiments of the invention may find their mostimmediate use in the form of improved ophthalmic devices, systems, andmethods. Exemplary embodiments of the present invention provide improvedophthalmic lenses (including, for example contact lenses, intraocularlenses (IOLs), corneal implants and the like) and associated methods fortheir design and use. Embodiments of the present invention may be usedwith monofocal diffractive or refractive lenses, bifocal diffractive orrefractive lenses, and multifocal diffractive or refractive lenses, e.g.embodiments of the present invention could be added to the oppositesurface of multifocal IOLs, e.g. TECNIS Multifocal or REZOOM or RESTORIOLs. In other words, an extended depth of focus feature may be addedto, for example the opposite surface of a diffractive or refractivemultifocal embodiment.

In addition, an extended depth of focus feature may be added to, forexample, a toric IOL, an IOL that modifies ocular spherical and/orchromatic aberration, and/or an accommodating IOL. In general, anextended depth of focus feature may be added to an IOL that modifiesocular aberrations.

Reading is often done in bright light conditions in which the pupil issmall. In contrast, night-time driving is done in low light conditionsin which the pupil is large. Embodiments of the present inventionencompass lenses that relatively emphasize intermediate or near visionfor small pupil sizes, while also relatively emphasizing far vision forlarge pupil sizes. In some such ophthalmic lenses, a greater proportionof light energy may be transmitted to the far focus from a peripheralportion of the lens to accommodate for low light, far viewing conditionssuch as night time driving, with the near or intermediate viewingreceiving relatively more light energy from a central portion of thediffractive profile—for reading or computer work for example and/or toprovide depth of focus and intermediate or near viewing under low lightreading conditions as in for example reading restaurant menus.

FIG. 1A is a cross-sectional view of an eye E fit with a multifocal IOL11. As shown, multifocal IOL 11 may, for example, comprise a bifocalIOL. Multifocal IOL 11 receives light from at least a portion of cornea12 at the front of eye E and is generally centered about the opticalaxis of eye E. For ease of reference and clarity, FIGS. 1A and 1B do notdisclose the refractive properties of other parts of the eye, such asthe corneal surfaces. Only the refractive and/or diffractive propertiesof the multifocal IOL 11 are illustrated.

Each major face of lens 11, including the anterior (front) surface andposterior (back) surface, generally has a refractive profile, e.g.biconvex, plano-convex, plano-concave, meniscus, etc. The two surfacestogether, in relation to the properties of the surrounding aqueoushumor, cornea, and other optical components of the overall opticalsystem, define the effects of the lens 11 on the imaging performance byeye E. Conventional, monofocal IOLs have a refractive power based on therefractive index of the material from which the lens is made, and alsoon the curvature or shape of the front and rear surfaces or faces of thelens.

In a young, healthy eye contraction and relaxation of ciliary muscles 17surrounding the capsular bag 14 contribute to accommodation of the eye,the process by which the eye increases optical power to maintain focuson objects as they move closer. As a person ages, the degree ofaccommodation decreases and presbyopia, the diminished ability to focuson near objects, often results. A patient may therefore conventionallyuse corrective optics having two optical powers, one for near vision andone for far vision, as provided by multifocal IOL 11.

Multifocal lenses may optionally also make special use of the refractiveproperties of the lens. Such lenses generally include different powersin different regions of the lens so as to mitigate the effects ofpresbyopia. For example, as shown in FIG. 1A, a perimeter region ofrefractive multifocal lens 11 may have a power which is suitable forviewing at far viewing distances. The same refractive multifocal lens 11may also include an inner region having a higher surface curvature and agenerally higher overall power (sometimes referred to as a positive addpower) suitable for viewing at near distances.

Rather than relying entirely on the refractive properties of the lens,multifocal diffractive IOLs or contact lenses can also have adiffractive power, as illustrated by the IOL 18 shown in FIG. 1B. Thediffractive power can, for example, comprise positive or negative addpower, and that add power may be a significant (or even the primary)contributor to the overall optical power of the lens. The diffractivepower is conferred by a plurality of concentric diffractive zones whichform a diffractive profile. The diffractive profile may either beimposed on the anterior face or posterior face or both.

The diffractive profile of a diffractive multifocal lens directsincoming light into a number of diffraction orders. As light 13 entersfrom the front of the eye, the multifocal lens 18 directs light 13 toform a far field focus 15 a on retina 16 for viewing distant objects anda near field focus 15 b for viewing objects close to the eye. Dependingon the distance from the source of light 13, the focus on retina 16 maybe the near field focus 15 b instead. Typically, far field focus 15 a isassociated with 0^(th) diffractive order and near field focus 15 b isassociated with the 1^(st) diffractive order, although other orders maybe used as well.

Multifocal ophthalmic lens 18 typically distributes the majority oflight energy into the two viewing orders, often with the goal ofsplitting imaging light energy about evenly (50%:50%), one viewing ordercorresponding to far vision and one viewing order corresponding to nearvision, although typically, some fraction goes to non-viewing orders.

In some embodiments, corrective optics may be provided by phakic IOLs,which can be used to treat patients while leaving the natural lens inplace. Phakic IOLs may be angle supported, iris supported, or sulcussupported. The phakic IOL can be placed over the natural crystallinelens or piggy-backed over another IOL. It is also envisioned that thepresent invention may be applied to inlays, onlays, accommodating IOLs,spectacles, and even laser vision correction.

FIGS. 2A and 2B show aspects of a standard diffractive multifocal lens20. Multifocal lens 20 may have certain optical properties that aregenerally similar to those of multifocal IOLs 11, 18 described above.Multifocal lens 20 has an anterior lens face 21 and a posterior lensface 22 disposed about optical axis 24. The faces 21, 22 of lens 20typically define a clear aperture 25. As used herein, the term “clearaperture” means the opening of a lens or optic that restricts the extentof a bundle of light rays from a distant source that can be imaged orfocused by the lens or optic. The clear aperture is usually circular andis specified by its diameter, and is sometimes equal to the fulldiameter of the optic.

When fitted onto the eye of a subject or patient, the optical axis oflens 20 is generally aligned with the optical axis of eye E. Thecurvature of lens 20 gives lens 20 an anterior refractive profile and aposterior refractive profile. Although a diffractive profile may also beimposed on either anterior face 21 and posterior face 22 or both, FIG.2B shows posterior face 22 with a diffractive profile. The diffractiveprofile is characterized by a plurality of annular optical zones orechelettes 23 spaced about optical axis 24. While analytical opticstheory generally assumes an infinite number of echelettes, a standardmultifocal diffractive IOL typically has at least 9 echelettes, and mayhave over 30 echelettes. For the sake of clarity, FIG. 2B shows only 4echelettes. Typically, an IOL is biconvex, or possibly plano-convex, orconvex-concave, although an IOL could be plano-plano, or otherrefractive surface combinations.

FIGS. 3A and 3B are graphical representations of a portion of a typicaldiffractive profile of a multifocal lens. While the graph shows only 3full echelettes, typical diffractive lenses extend to at least 9echelettes to over 32 echelettes. In FIG. 3A, the height of the surfacerelief profile (from a plane perpendicular to the light rays) of eachpoint on the echelette surface is plotted against the square of theradial distance (r² or ρ) from the optical axis of the lens. Inmultifocal lenses, each echelette 23 may have a diameter or distancefrom the optical axis which is often proportional to √n, n being thenumber of the echelette 23 as counted from optical axis 24. Eachechelette has a characteristic optical zone 30 and transition zone 31.Optical zone 30 has a shape or downward slope that may be linear whenplotted against ρ as shown in FIG. 3A. When plotted against radius r,optical zone 30 has a shape or downward slope that is parabolic as shownin FIG. 3B. As for the typical diffractive multifocal lens, as shownhere, all echelettes have the same surface area. The area of echelettes23 determines the add power of lens 20, and, as area and radii arecorrelated, the add power is also related to the radii of theechelettes.

As shown in FIGS. 3A and 3B, transition zone 31 between adjacentechelettes is sharp and discontinuous. The height of the lens facesharply transitions from sloping steadily downwards to steppingvertically upwards, and the transitions abruptly back to slopingsteadily downwards again. In doing so, echelettes 23 also have acharacteristic step height 32 defined by the distance between the lowestpoint and height point of the echelette. Hence, the slope (or firstderivative) and/or the curvature (second derivative) of the diffractivesurface are discontinuous adjacent the transitions.

Structure of Central Echelette

FIG. 4 provides a graphical representation of a cross section of aportion of an exemplary lens illustrating the central echelettestructure. The lens profile 200 has a ring diameter of 1.21 mm and astepheight at 220 of 2.05 μm, corresponding with a phase delay of 0.5lambda (see table 2). In this example, the ring diameter was reducedfrom 1.5mm (which is the inner ring diameter for a 2.0 Diopterconventional IOL diffractive lens) to 1.21 mm by a scaling factor √2, asdescribed in patent U.S. Pat. No. 5,121,980 (Cohen). Only the innerportion and part of the outer portion of half of the lens is shown,although since the lens is rotationally symmetric, the other half is amirror image.

The adjacent echelette(s) in the outer portion (not shown) are detailedbelow. Profile 200 includes an inner portion 210 or single ring, a stepor transition 220, and an outer portion 230. The outer portion 230extends beyond that disclosed in FIG. 4F to 2.5 mm and may be comprisedof limited additional echelettes Inner portion 210 extends between acentral location 210 of profile 200 and transition 220. Outer portion230 extends between transition 220 and a peripheral location (notshown). In some cases, transition 220 can be disposed at a distance fromthe optical axis that is within a range from about 0.5 mm to about 2.0mm, and peripheral location can be disposed at a distance from theoptical axis that is within a range from about 2.0 to about 3.5 mm, orbigger (for example, for contact lenses, the ranges would beapproximately 15% larger due to the optically more powerful position ofcontact lens compared to an IOL; those skilled in the art wouldappropriately scale certain dimensions depending on the application).

The inner portion or echelette 210 includes a center 210 a and aperipheral edge 210 b. At center or central section 210 a of innerportion 210 where radial distance is zero, the sag (d) of inner portionis between the sag (d) of the diffractive base curve 240 and the sag (d)of the peripheral curve 260 at 1.03 μm from the peripheral curve 260,corresponding with a phase delay of 0.25 lambda (see table 2). Atperipheral edge 210 b, the sag (d) of inner portion 210 is substantiallyequivalent to the sag (d) of diffractive base curve 240 at 13.8 μm. Thevalue of sag (d) between radial distance zero and radial distance at theperipheral edge 210 b at 0.61 mm, gradually and smoothly changes from1.03 μm (at r=0) to the value of the base curve 240 (at r=0.61 mm) whichis 13.8 μm. This change occurs in a parabolic fashion. As shown here,inner portion can present a parabolic shape, for example as described inEquation 4a of Cohen, Applied Optics, 31:19, pp. 3750-3754 (1992),incorporated herein by reference.

At the peripheral edge 210 b where the radial distance (r) is 0.61 mm,the value of sag (d) steps or changes from the value of diffractive basecurve 240 to the value of peripheral curve 260. Where radial distance(r) corresponds to transition 220, sag (d) of inner portion isequivalent to the value of the diffractive base curve 240. Relatedly,the displacement of the profile approaches that of the diffractive basecurve as the radial distance increases from a value of zero to a valueof about 0.61 mm. The stepheight is 2.05 μm resulting in a phase delayof 0.5.

The outer portion 230 includes an inner or central edge 230 a and aperipheral edge (not shown). At inner edge 230 a, the sag (d) of outerportion is substantially equivalent to the sag (d) of peripheral curve260. At peripheral edge, the sag (d) of outer portion remainssubstantially equivalent to the sag (d) of peripheral curve 260. Asdetailed below, a limited number of echelettes may be located betweeninner edge 230 a and peripheral edge.

FIG. 4A provides a graphical representation of a portion of a lensdiffractive profile with a central echelette and one peripheral adjacentechelette according to embodiments of the present invention. In FIG. 4A,the height of the surface relief profile (from a plane perpendicular tothe light rays) of each point on the echelettes surface is plottedagainst the distance from the optical axis of the lens. The echelettescan have a characteristic optical zone 930 and transition zone 931.Optical zone 930 can have a shape or downward slope that may be linearwhen plotted against p as shown in FIG. 4A. When plotted against radiusr, optical zone 930 can have a shape or downward slope that isparabolic. Central and peripheral echelettes can have a surface areathat is between 1 and 7 mm². For example, the echelettes may have asurface area that is 2.3 mm². An outer (refractive) zone can follow thebase radius with a fixed offset.

As shown in FIG. 4A, transition zones 931 between the optical zones 930and the adjacent optical zones can be sharp and discontinuous.Similarly, a vertical transition between adjacent echelettes and alsothe peripheral portion or refractive zone can be sharp anddiscontinuous. The height of the lens face sharply transitions fromsloping steadily downwards (e.g. across optical zones 930) to steppingvertically upwards (e.g. at transition zone 931), and the transitionsabruptly back to sloping steadily downward or substantially horizontalat outer refractive zone. In doing so, echelette 930 also has acharacteristic step height 932 defined by the distance between thelowest point and highest point of the echelette. Hence, the slope (orfirst derivative) and/or the curvature (second derivative) of thediffractive surface are discontinuous adjacent the transition. The firstderivative can be indicated by the direction of the lines, and thesecond derivative can be indicated by the curve of the line.

According to some embodiments, light comes from below, in the directionindicated by arrow A, and only hits the echelettes 930 of the profile.According to some embodiments, in theoretical terms light does not hitthe vertical connection of the optical zones, and hence the profile canbe said to have no transition zone. According to some embodiments, inpractice when one attempts to produce such a profile, for instance bylathe cutting, it may be difficult to reproduce the sharp corner (e.g.at where the optical zone connects with the adjacent optical zone) andhence the corner may be rounded to some extent due to the finite chiselradius. Such rounding may have a negligible effect on the opticalperformance. According to related embodiments, transition zone 931,which can be referred to as the transition from the echelette to theadjacent zone or zones, can be shaped in a specific way, so as tooptimize the optical performance, for example to minimize scatter from asharp transition.

PROFILE PARAMETERS

The profile design can be characterized in terms of a set of parameters.For example, the limited echelette profile can be described as having acentral echelette with a diameter and surface area, an adjacentechelette(s) with the same surface area, and an associated stepheight ateach transition resulting in a phase delay. The central echelette mayhave a diameter within a range from about 1 mm to about 5 mm. Forexample, the central echelette may have a diameter of about 1.5 mm.Central echelette may have a surface area that is between 1 and 7 mm².For example, the central echelette may have a surface area that is 2.3mm². The peripheral echelette(s) may have a surface area equal to thecentral echelette. In particular, Table 1 discloses the dimensions ofthe radius and diameter of the central echelette, along with the surfacearea of the central and peripheral echelettes.

R (mm) De (mm) Area (mm²) 1.48 3 6.9 1.05 2.1 3.5 0.86 1.7 2.3 0.74 1.51.7 0.66 1.3 1.4 0.61 1.2 1.2

The step height or profile height can determine the phase delay or phaseshifting profile. A greater step height can correspond to a greaterphase shift. According to some embodiments, a lens can include atransition characterized by a step height producing a phase shiftbetween about 0.25 and about 1 times the design wavelength. In somecases, a diffractive profile can be characterized by a designwavelength, and the lens can include a transition characterized by astep height producing a phase shift between about 0.15 and about 2 timesthe design wavelength. According to some embodiments the lens mayinclude a transition characterized by a step height producing a phaseshift of about 0.5. In other embodiments, the lens may include atransition characterized by a step height of about 0.4.

Table 2 provides dimensions of various samples disclosing therelationship between phase delay (in wavelengths) and step height (inμm), as valid for an example IOL material.

TABLE 2 Phase Delay Stepheight 0.896 3.68 0.700 2.87 0.590 2.42 0.5092.09 0.500 2.05 0.423 1.74 0.366 1.50 0.350 1.44 0.250 1.03 0.150 0.62

FIG. 4B provides a graphical representation of a portion of a lensdiffractive profile with a central echelette and two peripheralechelettes according to embodiments of the present invention. The heightof the surface relief profile (from a plane perpendicular to the lightrays) of each point on the echelettes surface is plotted against thedistance from the optical axis of the lens. According to someembodiments, a lens with a central and peripheral adjacent echelette, asdisclosed in FIG. 4A may also be comprised of an additional peripheralechelette with a refractive region between the outermost echelette andthe interior echelettes.

FIG. 4C also details a portion of a lens diffractive profile with acentral echelette and two peripheral echelettes. In this embodiment,however, the refractive zone is immediately adjacent to the centralechelette and separates the central echelette from three peripheral andadjacent echelettes.

Although the above preferred embodiments disclose lenses with echelettesthat have equal stepheights, lenses with echelettes with varyingstepheights are also covered herein as detailed in FIG. 4D. FIG. 4D.discloses a four echelette embodiment wherein a refractive regionseparates the central and adjacent echelette from three peripheraladjacent echelettes. As seen in FIG. 4D, the stepheight (defined by thedistance between the lowest point and highest point of the echelette) ofthe three outer echelettes is less than the stepheight of the innerechelettes. Of course, in addition to covering embodiments where thestepheight of the outer echelette(s) is less than the innerechelette(s), the stepheight of the inner echelette(s) may be less thanthe outer echelette(s). It is also foreseeable, that the inner and outerechelettes may all have varying stepheights whether the stepheights beincreasing, decreasing, or alternating.

FIG. 4E provides a graphical representation of a portion of a lensdiffractive profile with a central echelette and a peripheral echelettewhich is not adjacent to the central echelette. The central echelettemay have a shape or downward slope that is parabolic. A refractiveregion may then separate the central echelette from the peripheralechelette. The peripheral echelette may then be characterized by a sharpand discontinuous stepheight followed by a downward slope. As in theembodiments above, a peripheral refractive region may surround theoutermost echelette. Additionally, other exemplary embodiments includenon-adjacent echelette variations analogous to FIG. 4A-4D. By way ofnon-limiting example, two echelettes that are not separated by arefractive region may also be non-adjacent.

Pupil Dependence

The size of the human pupil varies with illumination. In bright lightthe pupil is small, and in dim or low light conditions the pupil islarge. In addition, the size of the human pupil varies withaccommodative effort. Without accommodative effort, the pupil is largerthan with accommodative effort. Hence, for a smaller pupil, it may bedesirable to provide a design that places a relative emphasis onintermediate or near vision. For a larger pupil, it may be desirable toprovide a design that places a relative emphasis on far vision.

In typical reading or near vision conditions where the light is bright,the size of the pupil is small, e.g. between about 1 mm and 2 mm indiameter, and the eye has a large depth of focus (for example from apinhole effect), almost irrespective of the optics of the IOL. When thesize of the pupil is large, e.g. larger than about 4-5 mm in diameter,the situation generally applies to low light conditions, and is oftenassociated with distance vision for which the power of the IOL istypically established. Therefore, many patients would benefit most froman IOL that enhances the depth of focus in order to view at intermediatedistances. An IOL having a central echelette with limited adjacentechelettes may effectively increase the depth of focus for intermediatepupil sizes, while maintaining the general increased depth of focus ofsmall pupil sizes, and also maintaining an emphasis on far vision forlarge pupil sizes.

At the same time, since the limited echelettes and the remaining surfacearea of the optic or remaining lens portion (“non-echelette”) haveunequal surface areas for almost all pupil sizes, there is an incompletesplit between the foci. The condition of dysphotopsia (e.g. halos) thatis present for multifocal lenses is observed to be dominated byseparation of two foci and pupil size effects. Accordingly, pursuant toexemplary embodiments of the present invention, the lens may includeonly a limited number of echelettes, so that light separation betweendistinct foci is not complete, as compared to standard diffractivemultifocal IOLs. Since the split of light is incomplete, the separationof foci is incomplete. The incomplete separation of foci contributes tothe extended depth of focus and the attenuation of dysphotopsia (e.g.halos).

In an exemplary embodiment, the limited echelette design has an opticalperformance that depends on the pupil size. For very small pupils, wherethe pupil is smaller than the size of the central and adjacentechelette(s), the echelette will act as a refractive lens, having a verylarge depth of focus due to the pinhole effect. For medium and higherpupil sizes, where the pupil covers the central echelette and theadjacent echelette, the lens will act as a diffractive/refractive lens,directing the light to several foci. For higher pupil sizes, more lightis being directed to the lower order foci. The size of the central andadjacent echelette(s) influences the pupil dependence of the lens. Assuch, the size of the central and adjacent echelette(s) can be chosen,depending on the pupil sizes of a specific patient. For example, thepupil sizes of a patient may be measured in bright light, in dim light,during far vision and during near vision, and in the differentcombinations of light level and accommodative effort. These differentpupil sizes, which may be defined as pupil dynamics, can be used asinput parameters for an optimal design of the limited echelette design.

For example, if a patient has a pupil diameter during near vision (e.g.viewing target at close distance, with high accommodative effort)smaller than 2 mm, having this pupil dimension with both bright and dimlight, then the size of the central and adjacent echelette(s) may beselected to be smaller than 2 mm (e.g. outer diameter of the adjacentechelette of FIG. 4A), as to provide adequate near and intermediatevision. Relatedly, if a patient has a pupil diameter during near visionlarger than 2 mm, having this pupil dimension with both bright and dimlight, then the size of the central and adjacent echelette(s) may be 2mm or larger, as to provide adequate near and intermediate vision. Ingeneral, the diameter of the central and adjacent echelette(s) can besmaller than the smallest pupil size the patient has under any condition(e.g. bright/dim light; near/far vision). For any type of pupildynamics, the size, the profile, and the offsets may be chosen tomaximize the lens performance for that specific patient, or group ofpatients. Generally, this is a trade off between the different visioncircumstances (combinations of light level and accommodative effort) atwhich the pupil of the patient is measured. Accordingly, exemplaryembodiments include a method of designing an ophthalmic lens comprisedof utilizing pupil size measurements and based on the measurementsdetermining the size of an isolated echelette to impose on the surfaceof a lens. The pupil size measurements may be based on a group ofpatients.

EVALUATION OF VARIATIONS OF A SPECIFIC EXAMPLE

FIGS. 5 and 6 show calculated defocus curves in the ACE eye model of anembodiment with a central ring diameter of 1.48 mm, an echelette surfacearea of 1.7 mm², and a phase delay of 0.4 wavelength. The horizontalaxis denotes the defocus value in the image plane, in millimeters.Negative defocus values represent the myopic eye, and therefore,simulate vision at intermediate and near distances. The vertical axisdenotes the modulus (MTF) at 50 cycles per millimeter. Data for 5 mmpupil diameters is included. FIG. 5 shows the defocus curve for anembodiment having only a single central echelette. FIG. 6 shows anexemplary embodiment as disclosed in section 4E, having, in addition tothe central echelette, a peripheral echelette. The peripheral echeletteand has a surface area of 3.5 mm², and a phase delay of 0.82 wavelength.The MTF at intermediate vision distances, with defocus values of about−0.2 mm to −0.3 mm, as shown in FIG. 6 is higher than the MTF atcorresponding defocus values in FIG. 5. As illustrated in the figures, acentral plus peripheral echelette increases the depth of focus ascompared to a central echelette only.

Embodiments of the present invention may be combined with a multifocallens design, and with that extend the depth of focus of each focus ofthe multifocal lens. Similarly, embodiments of the present invention maybe combined with an accommodating lens design, by which the range ofaccommodation of the accommodating lens can be extended. In addition,embodiments of the present invention may be combined with lensescorrecting ocular aberrations, like toric lenses, aspherical lenses,lenses correcting chromatic aberrations, and the like.

Embodiments of the present invention may be combined with a lens designcorrecting chromatic aberrations. In one embodiment, the phase delay ofthe echelettes in the preceding examples is increased by a discretemultiple of wavelengths, in order to correct for chromatic aberration.For example, if a phase delay of 0.5 was used, corresponding to astepheight of 2.05 μm, an alternative embodiment would have a phasedelay of 1.5, corresponding to a stepheight of 6.15 μm. This embodimentdirects the first order diffraction to the far focus, and the secondorder diffraction establishes the depth of focus at the intermediate andnear range.

While the exemplary embodiments have been described in some detail, byway of example and for clarity of understanding, those of skill in theart will recognize that a variety of modification, adaptations, andchanges may be employed. Hence, the scope of the claims should not belimited to the description of the preferred versions contained herein.

What is claimed is:
 1. An ophthalmic lens, comprising: an anterior faceand a posterior, the faces disposed about an optical axis; and at leastone diffractive profile imposed on the anterior face or the posteriorface, the at least one diffractive profile consisting of an innerechelette and 1 or 2 peripheral echelettes.
 2. The ophthalmic lens ofclaim 1, wherein at least 2 echelettes are not adjacent to each other.3. The ophthalmic lens of claim 2, wherein the at least 2 echelettesthat are not adjacent to each other are separated by a refractiveregion.
 4. The ophthalmic lens of claim 2, wherein the at least 2echelettes are not separated by a refractive region.
 5. The ophthalmiclens of claim 1, wherein the inner echelette and the peripheralechelette(s) are not separated by a refractive region.
 6. The ophthalmiclens of claim 1, wherein the echelettes are characterized by a surfacearea between 1 and 7 square millimeters.
 7. The ophthalmic lens of claim1, wherein the echelettes have the same surface area.
 8. The ophthalmiclens of claim 5, wherein the inner echelette has a diameter within arange from about 1 mm to about 5 mm.
 9. The ophthalmic lens of claim 1,wherein the lens further comprises a peripheral portion characterized bya spherical curve or an aspherical curve.
 10. The ophthalmic lens ofclaim 1, wherein the echelettes further comprise of transitionscharacterized by a step height having a value within a range from about0.5 μm and about 4 μm.
 11. The ophthalmic lens of claim 9, wherein thestep heights provide a phase shift between about 0.25 and about 3 timesthe design wavelength.
 12. The ophthalmic lens of claim 10, wherein thestepheight for at least 2 echelettes differ.
 13. The ophthalmic lens ofclaim 10, wherein the surface area for at least 2 echelettes differ.